This invention relates to improvements in apparatus for suppressing infrared emission.
As acknowledged by the prior art, the successful flight of high altitude military aircraft is dependent, in part, upon the ability of the aircraft to remain undetected during flight. Unfortunately, the gas stream discharge from a gas turbine engine is a high temperature gas mixture. Because of their high temperatures, the exhaust gases and the hot metal walls directly in contact with the hot gases, are excellent sources of infrared energy to be detected. Hence, against the highly sophisticated infrared sensors developed during recent years, particularly for military use, an aircraft powered by a gas turbine engine is at a particular disadvantage. Attempts have been made to reduce infrared emission in gas turbine engines by the use of various cooling assemblies; and the most effective arrangements have been those designed to cool the hot metal walls. However, the hot gas plume is still a prime source of infrared radiation. Most exhaust cooling designs entail either too great a power loss in operation, or a high degree of complexity and weight.
A particularly effective infrared suppressor is described in U.S. Pat. No. 3,210,934. In this apparatus a jet engine exhaust nozzle known as the plug type is described. The walls of the exhaust passage, that is, the outer engine casing walls, and the plug walls, are cooled by either ambient ram air or by engine bypass air. This bypass air, which is substantially cooler than the exhaust gases, also mixes with the exhaust gases to lower the turbine exit gas temperature.
In accordance with the practice of this invention, additional cooling means for jet engine exhaust nozzles of the plug type are provided which utilize nonaerodynamic space. This invention, therefore, effectively and simply increases heat exchange relationships in plug type infrared radiation suppressors without significantly penalizing engine power during suppressor operation.